FRD - Investigación - Ciencia y Tecnología

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Author: search.filters.author.Scarpettini, AlbertoSubject: search.filters.subject.metallic nanostructures

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    High resolution imaging using nanoparticle based probes
    (2018) Scarpettini, Alberto; Bragas, Andrea
    New plasmonic probes, based on silica microspheres decorated with metal nanoparticles (Figure 1), are built and used to confine and enhance the electric field in their interaction with the sample, giving ultra-high optical resolution in a wide variety of samples [1]. The coverage and aggregation processes of nanoparticles on plane and spherical substrates were systematically studied [2]. These probes present red shifted resonances, dominated by the formation of small nanoparticle clusters [3]. Approach curves with the new probes show clearly field enhancement at very short probe-sample distances, and depend strongly on the incoming wavelength and polarization. Optical contrast was achieved in flat samples composed by materials of different dielectric constants, and images were obtained using optical feedback.
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    Nanorod-based plasmonic substrates with predefined optical resonances
    (2018) Scarpettini, Alberto; Gutierrez, Marina
    To design and fabricate plasmonic substrates to be used in ultrasensitive chemical sensing or surfaceenhanced spectroscopies, it is important to achieve control on the morphology, dimensions and surface density of metallic nanostructures on the substrate, and therefore to achieve control on their optical resonances. In this direction, monodisperse colloidal gold nanorods were synthesized in a seed-mediated growth [1] with a longitudinal surface plasmon resonance tunable in wavelengths from 600 to 1000 nm. These nanorods with well-controlled size and aspect ratio were used as plasmonic building blocks. Glass substrates were chemically modified and the synthesized gold nanorods were adsorbed through a dipping process [2]. The nanostructured coverage dynamics of these substrates was characterized by spectrophotometry and electron microscopy (Fig. 1). A nanoparticle surface aggregation was observed during the coverage process at long times. This aggregation is dominated by the mobility of the isolated nanorods, which first join in dimers and, further in time, in clusters of higher number of nanorods, changing from well-defined longitudinal plasmons to more complex coupling resonances. Evolution of amplitudes of resonance peaks in extinction spectra and nanorod counting statistics were used to model both coverage and aggregation processes [3]. Their characteristic times and saturation values were analyzed and related with kinetic parameters and nanorod extinction coefficients. This work can be used as a predictive tool to prepare plasmonic substrates with desired optical resonances.